Electric lamp for use in mines



sepi- 1929- w. M. THORNTON 1,727,185

ELECTRIC LAMP FOR USE IN MINES Filed Sept. 224, 1928 fi e/2 72/; WM, WORN-ray Patented Sept. 3, 1929.

UNITED STATES WILLIAM MUNDELL THORNTON, OF NEWCASTLE-UPON-TYNE, ENGLAND.

ELECTRIC LAMP FOR USE IN MINES.

Application filed September 24, 1928, Serial No.

This invention relates to an electric lamp for use in mines and other places where inflammable gas is likely to be present. Y

It is well known that an electrically-heated filament or like member attains a higher tempe; ature in certain inflammable mixtures than in air. Various forms of gas detecting and measuring instruments have been proposed depending upon this fact and, in different ways, comparin the effects produced by such filaments with those due to a similar filament sealed in air. It is to this broad type of apparatus that the present invention relates more particularly.

It has been proposed to provide in a miners electric lamp two filaments, one whose brightness is not affected by the presence of inflammable gas and the other having in series with it a conductor whose resistance is varied,

usually through the well known catalytic effeet, by the resence of such gas and to bring both such laments to the same degree of luminosity by adjusting a resistance in series with the unafiected filament and by so doing obtaining an indication of the proportion of inflammable gas present. 4

The present invention also depends u on the comparison of the luminosity of two laments, one affected and the other unaffected by the presence of inflammable gas, but the comparison is actually between a sealed filament and an exposed filament such exposed filament glowing more brightly owing to the burning of the inflammable gas at its surface.

The improved lamp according to the present invention comprises two electricallyheated filaments, one sealed in air and normally used for illumination and the other exposed to the atmosphere under test, the two filaments being mounted near each other, a variable resistance contained in the lamp casing and means for adjusting such resistance by the relative movement of two parts of the casing to cause the two filaments to glow with equal luminosity, the amount of such movement indicating the percentage of inflammable gas present.

The sealed and exposed filaments are adj a cent to each other in an appropriate chamber on in the lamp so that at any time the relative luminosity or the amount of glow or redness of the two filaments can be compared. The

normal or zero adjustment of the apparatus is such that the luminosities of the two fila- 5 ments are equal when the exposed filament is in air. When taken into an atmosphere con- 308,025, and in Great Britain October 11. 1927.

taining up to certain proportions of inflammable gas the exposed filament will '.e raised in temperature owing to the combustion of the mixture at its surface and its glow is therefore increased. This is observed and the variable resistance is adjusted to alter the relative values of the currents in the two filaments until their luminosities are again equal.

The variable resistance may be in series with the sealed filament those two members being in parallel with the exposed filament in a battery circuit.

01' again, the two filaments may be in series in the battery circuit and the variable resistance ma be as a shunt across the sealed filament. fter zero adj ustmcnt in air increased brightness of the exposed filament in gas is balanced by adjusting'the shunt resistance,

the movement for making this adjustment indicating the proportion of gas present. In each of these constructions there may he a separate resistance provided for the initial adjustment of the currents through the tilaments.

In the accompanying drawings,

Figure l is an elevation partly in section of one construction of miners electric lamp according to this invention,

Figure 2 is a portion of a similar View taken at right angles to Figure 1,

Figure 3 is an under plan of the upper part or cap of the lamp casing,

Figure 4 shows the electric circuit of the lamp,

Figure 5 is a dia ram of the circuit in conventional form, and v Figure 6 is a diagram of an alternative circuit.

With reference first to Figures 1 to 4, the lamp as a mechanical structure comprises main parts which are known in miners electric lamps, namely a casing A containing a battery B and a rotatable ca 3 or casing C on which is mounted a lamp bulb D surrounded by a protective glass E. In the improved lamp there is mounted adjacent to the bulb D containing the sealed filament D another filament F held between two supports F to which filament the atmosphere under test has access through a wire gauze G.

One terminal of each of the filaments D and F is connected to a central pin H which makes contact with the pole B of the battery B. The other terminal of the sealed filament D is joined to a small contact plate D and the other terminal of the exposed filament F to another contact plate D these two plates D and I) being mounted on the underside of a plate C of insulating material forming part of the rotatable cap C.

Held in a recess in this plate C is a spiral resistance J and the second polo B of the battery has contacts which make rubbing connection with the plate I) and with the resistance J. One end of that resistance is connected to the plate I) and the other end is free. These connections are best seen in Figure .l: where I5 and 13* represent the rubbing contacts connected to the poles of the battery.

If these contacts lie in the gap J shown in Figure 4 the connection to the battery is broken. If the casing be rotated slightly to bring the contact B7 on to the plate I) the sealed filament D will be com'iected straight across the battery and will be fully bright. The exposed filament F will not be in circuit. In this position the lamp functions as a miners electric lamp in the ordinary way. It

the presence of gas is suspected the casing is rotated so that the contact li makes contact with the free end of the variable resistance J in which position the contact li makes connection with the adjacent end of the plate I). In this position the exposed filament F .is connected straight across the battery and it will glow more or less ln'ightly according to the amount of gas present. At the same time the sealed filament is connected in series with the resistance J across the battery. If gas is present the exposed filament will be brighter than the sealed filament and the casing is then rotated so as to cut out more and more of the variable resistance J until the filament D glows as brightly as the exposed filament F. At that point the registration of suitable marks on the. rotatable cap C with some point on the casing A will enable the percentage of gasprcsent to be read. Any convenient arrangement of scale and pointer may be provided for reading these percentages but in the example illustrated the cap 0 is provided with a raised scale indicating percentages. As may be seen from Figure 2 there is a raised 0 forzero and screw heads arranged to indicate 1, 2, 3 and 4 by the sense of touch. The

registering point on the casing is constituted by a milled head A. This milled head is not permanently fixed on the casing but is meanted on a band or ring A which can be turned relatively to the casing and clamped thereto by the milled head. This arrangement is provided so that the position of the milled head may be altered relatively to the casing for purposes of adjustment to allow for variations in the voltage of the battery.

The engagementbetween the casing A and the cap C is by means of a screwthread and to prevent any possibility of the two parts beingseparated when the lamp is in usein the mine a spring plunger O is mounted on the cap so thatfthe cap can not normally be turned relatively to the casing for more than one revolution, as the end of the plunger comes in contact with a stop C (Figure 1). This plunger C may be locked in any conveni-cnt way (not indicated inthe drawings) before the lamp is given out to the miner.

Figure 5 is merely a diagram showing in a conventional and simple liorm an electric circuit for gas-detecting apparatus accord ing to this invention. In this diagram the exposed filament F is in parallel with the sealed filament D plus a variable resistance J and the battery 13'' supplies current to both when a switch K is closed. The resistance J is varied to make the brightness oi the sealed filament- D correspond to that of the exposed filament I when in a gaseous atmosphere and the percentage 01 gas is read oil on a scale moved over by the switch of the variable resistance J The arrangement corresponds in its essentials to that of the lamp described with reference to Figures 1 to 4, the only diiterence being that an additional resistance K is provided for the purpose of initial adjustment-or calibration before the lamp is issued for use. Such a resistance may be incorporated in the lamp previously described.

Figure (3 is a diagram ofan alternative circuit where the'sealed filament D is in series with the exposed filament F and has the variable resistance J 3 shunted across it.

IVhat I claim as my invention and desire to secure by Letters Patent is "A miners electric lamp comprising a easing adapted to contain a battery, a cap or cover rotatable relatively thereto, a sealed filament and an exposed filament mounted on said cap a resistance in. the cap, a central contact mounted on the cap connected to one end of said sealed filament and one end of said exposed filament and also to one pole of the battery, two contact plates mounted on the cap the first of such contact plates being connected to the other end of said sealed filament and to one end of said resistance and the other contact plate being connected to the other end of said exposed filament rubbing connections between the other pole of the battery and the second contact plate and the resistance, whereby relative rotation of said cap and easing will switch the exposed filament on and while it is on will also switch on the sealed filament in series with a variable amount of the resistance, and means whereby the relative rotation of the cap and casing will give an indication of the per centage of inflammable mosphere.

In testimony whereof'I have signed my name to this specification.

WVILLIAM MUNDELL THORNTON.

gas present in the at. 

